The operation of certain computer equipment can be negatively affected by the presence of environmental hazards, such as airborne contaminants. To prevent this harm from occurring, sensitive equipment may be housed in an enclosure that is designed to keep out airborne contaminants.
An example of sensitive equipment housed within a protective enclosure is a hard disk drive (HDD). An HDD is a non-volatile storage device, which is housed in a protective enclosure, that stores digitally encoded data on one or more circular platters having magnetic surfaces. When an HDD is in operation, each platter is rapidly rotated by a spindle system. Data is read from and written to a platter using a read/write head which is positioned over a specific location on a platter by an actuator.
A read/write head uses a magnetic field to read data from and write data to the surface of a platter. As a magnetic dipole field decreases rapidly with distance from a magnetic pole, the space between a read/write head and the surface of a platter must be tightly controlled. To provide a uniform distance between a read/write head and the surface of a platter, an actuator relies on air pressure inside the hard drive enclosure to support the read/write heads at the proper distance away from the surface of a platter while the platter rotates. A read/write head therefore is said to “fly” over the surface of a platter. That is, the air pulled along by a spinning platter forces the head away from the surface of the platter. When a platter stops spinning, a read/write head must either “land” or be pulled away. Airborne contaminants, such as dust, can distort the surface of either a read/write head or a platter. Very small airborne particles, such as the size of a few microns, may distort the surface of either a read/write head or a platter. When the surface of either a read/write head or a platter becomes distorted, it is more likely that a read/write head may scrape across the surface of a platter, which may grind away the thin magnetic film of the platter and cause data loss and potentially render the HDD inoperable.
When a HDD is in operation, the air inside the enclosure of the HDD is constantly circulating due to the spinning of the platters. The circulating air typically passes through an internal recirculation filter to remove any contaminants that may be left over from manufacture, inadvertently introduced into the HDD enclosure, or generated internally in normal operation of the HDD.